standardize old ScalarFields test code

[dehann]

See ongoing error description at: #518 (comment)

[codecov]

Codecov Report

Merging #517 (489403e) into master (96aa6c3) will increase coverage by 1.90%.
The diff coverage is 2.56%.

@@            Coverage Diff            @@
##           master    #517      +/-   ##
=========================================
+ Coverage    1.16%   3.07%   +1.90%     
=========================================
  Files          47      49       +2     
  Lines        1978    2019      +41     
=========================================
+ Hits           23      62      +39     
- Misses       1955    1957       +2     

Impacted Files	Coverage Δ
src/services/RequiresImages.jl	0.00% <0.00%> (ø)
src/services/ScalarFields.jl	0.00% <0.00%> (ø)
src/RoME.jl	100.00% <100.00%> (ø)
src/TemporaryFunctionality.jl	10.52% <0.00%> (+10.52%)	⬆️
src/factors/Point2D.jl	23.07% <0.00%> (+23.07%)	⬆️
src/factors/PartialPose3.jl	38.57% <0.00%> (+24.07%)	⬆️
src/factors/Pose3Pose3.jl	59.09% <0.00%> (+59.09%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bf721e3...489403e. Read the comment docs.